my bestfriends stupid girlfriend....

okay so my bestfriend, lucien, has this really obnoxious girlfriend. everytime i talk to him onthe phone shes over. every time i talk to him in the hall, she comes out of no were. i feel like a have to keep my distance, because of there relationship, because his girlfriend sees me as a threat, and doesnt trust lucien. even though she has tried to cheat on him a couple of times. and he just forgave her. she doesnt deserve someone like lucien, and iv tried to tell him, but it doesnt do anything. i just want to be able to spend time with my best friend, and not have to worry about his stupid girl friend! any advice??? thank you guys xoxo(: